Electric fuze energy capsule



Aug. 2, 1966 GAY 3,264,500

ELECTRIC FUZE ENERGY CAPSULE Filed NOV. 19, 1964 I JNVENTOR, :Elen amtn A. Bag

BY" #4241? 7L Ma ZM United States atcnt 3,264,500 ELECTRIC FUZE ENERGY CAPSULE Benjamin A. Gay, Phoenixville, Pa., assignor to the United States of America as represented by the Secretary of the Army Filed Nov. 19, 1964, Ser. No. 412,580 Claims. (Cl. 310--3) The invention described herein may be manufactured and used by or for the Government for governmental purposes, without the payment to me of any royalty thereon.

This invention relates to radioactive power sources, and in particular to radioactive power sources having therein an electron emitting radioactive material.

Accordingly, it is an object of this invention to provide for an electric energy capsule which may be used as an energy source.

It is a further object of the instant invention to provide a device which includes in an assembly a unique cell which converts nuclear energy into electrical energy.

It is another object of the instant invention to provide in a cell an electrical capacitor for storing energy and to provide a voltage regulator within the cell which operates because of the Geiger effect in gas conductor. The cell thus provided can be equipped with a diaphragm switch for completion of an external circuit to which the energy may be delivered.

Briefly, the basic operation results from a central conductor emitting charged particles as a result of being coated by a radioactive emitting material. Some of the emitted particles cross an insulating material and arrive at an outer metal housing. The consequent separation of charge from the central conductor results in a capacitive eifect and this eiiect is an integral part ofthe unit. The voltage of the fully charged capacitor is regulated by the Geiger eflect in a sealed gas volume. The energy stored in the charged capacitor is delivered to an external circuit upon closure of a button switch.

Referring now to the figure in the accompanying drawings illustrating a longitudinal section of the device of the invention, a metal case 1 is provided, at the bottom end of which there is an opening 2. Housed within the metal case an end closure 3 comprising the electron collector is placed across the opening. Within the metal case, an insulator material 4 is packed against the end closure 3. Centrally positioned within the insulating material is a flared base 5 of a central conducting rod 6 which extends to and converges to a point 7 near the other end 8 of the metal case 1. The rod near the base thereof passes through a central opening 9 in a metal shield 10 which is also embedded in the insulating material. The base 5 of the rod is supported in the insulating material 4 by a bracket 11. The bottom side of the rod 12 the side facing the end 3, is coated with a radioactive material 12A such such as strontium 90. An insulator 13 encompasses the conducting rod near the pointed end of the rod previously designated 7, and the pointed tip extends therethrough into a chamber 14. The chamber 14 is consequently defined by the insulator 13 on one side and on the other side, the end 8 of the metal case 1. An opening 14A is provided in the top of the metal case and it is covered by a flexible insulating disc 15 which is positioned inside the metal case 1. A metal button 16 is slidably mounted in the flexible disc 15. In chamber 14 intermediate disc 15 and insulator 13 and supported therein by disc 15 and insulator 13 is a frusto-conical shaped ionization regulator disc 17. The regulator disc 17 has therein a central aperture 18 at the tip thereof, said aperture encompassing the pointed rod tip 7. Disposed in the metal case 1 between the insulating material 4 at the end 2 and the insulator 13 is a capacitor 19. The radioactive source, the emitting material, coated upon the bottom 12 of the rod 6 may be strontium or some other suitable material such as tritium. Strontium 90 is well suited as the radioactive coating because it decays by beta-emission to yttrium 90, and this in turn is decayed by further betaemission thereby increasing the effectiveness of a given amount of strontium.

In operation, the basic principles of which are further discussed hereinafter, a potential is developed across the capacitor and this may be released to an external circuit by depressing the button 16 in the flexible disc 15. This will establish contact with the metal point 7 on the rod 6, thereby completing a circuit. The metal shield 10 is provided to reduce external radiation, and also the radiation level in the capacitor. Any elfect of the radiation on the insulation resistance of the capacitor is thus reduced.

A fraction of the electrons emitted by the emitter material will reach the metal end 3. The fraction collected will depend on many factors, some important one being:

'the self absorption of the electrons at the source, absorption of the electrons by the insulating material, the energy spectrum of the emitted particles, the scattering of the electrons in the source and insulator, the geometry of the emitter and collector electrodes, and secondary emission of electrodes at the collector surface. As a result of this second factor in the foregoing enumeration, it is clear that the nature of the insulator 4 is important, as well as, the physical thickness of it. Further, because of the secondary emission of electrons at the collector surface, a net change in the collected charge can result.

As a consequence of these and other factors, a certain collection efiiciency, K, results, which is the fraction of particles emitted that are actually collected. If the dis integrations of the emitting material per second are designated D9 then the charge per second, or current, is KD.

This charging current is opposed by the ohmic discharge through the capacitor 19 which is connected between the central conductor 6 and the metal case 1. Because connection to the external circuit is not made until desired by depressing the button 16, external surface leakage due to humidity eflects and leakage to the external circuit is avoided. The aforesaid resistances can be lumped and called a leakage resistance, R; hence, the discharge leakage current is simply, V/R, when V is the instantaneous voltage across the capacitor 19. Thus the net charging rate of the capacitor dq/dt or, more simply, current, is equal to the algebraic sum of the charge and discharge currents, KD and (-V/R) respectively. When equilibrium is reached, i.e., the charging current is zero, the maximum voltage V is given by the equation V =RKD, where the symbols have the values as assigned above. However, because the factors RK and D are subjected to uncontrollable variations, it is desirable to regulate the voltage by some means. For this reason the chamber 14 is provided and contains a dry gas and the pointed end 7 of the conductor rod 6 protrudes therein. Also the ionization regulator disc 17 is provided within this space 14, the rod end 7 and the disc 17 can be designed as required, and, if the potential diflerence is great enough, a Geiger type breakdown will occur in the gas upon passage of a random ionizing ray. Such a ray might be a cosmic ray or a gamma-ray. The resulting partial discharge of the capacitor 19 and the rate of partial discharge increases with increasing potential differences, and the potential difference will therefore tend to remain at an equilibrium value that is below the maximum voltage described as the produce of RK/D.

After the initial charging period, the stored energy may be delivered at any time as an external circuit by depressing the button 16 which contacts the rod 6, and thus connects an external circuit.

The life time of this capsule is fundamentally limited by the lifetime of the radioactive source, and terminates when the amount of radioactive material remaining is no longer sufficient to maintain the aforesaid decay rate, D, at a sufiiciently high value. The voltage across the capacitor drops :below the regulated value, V, and steadily decreases at .a rate determined by the half-life period of the radioactive isotope. Other factors such as insulation deterioration may also affect the lifetime of the cell.

It is desirable to avoid as an emitting material radioactive substances which involve emission of gamma rays in order to keep the external radiation at a minimum.

While the instant invention has been shown and described herein in a preferred embodiment, it is recognized that departures may be made therefrom within the scope of the invention, which is therefore not to be limited to the details disclosed, but is to be awarded the full scope .of the claims.

What is claimed is:

1. In an energy capsule, a metal housing having an opening in the top and the bottom thereof, a flexible disc of insulating material having a central aperture covering the top opening, a metal plate covering the opening in the bottom of said housing, insulator material disposed in .the bottom of the housing adjacent said plate, a conductor -rod having a pointed tip and a flared bottom disposed ber is formed between said flexible disc and said insulator and a central chamber is formed between said insulator and said insulating material disposed in the bottom of said metal housing, a capacitor, said capacitor fixed in said central chamber and connected between said conductor rod and said metal housing, said pointed tip of the conductor rod protruding into said top chamber, and a metal button mounted in said flexible disc for movement into contact with said pointed tip.

2. An energy capsule as in claim 1 wherein said emitting material comprises strontium 90.

3. An energy capsule as in claim 1 wherein said top chamber has a frusto-conical shaped ionization regulator disc afiixed therein adjacent said flexible disc, the apex of said frustum extending to and encompassing said rod tip in spaced relationship, and wherein said top chamber is sealed and has therein a gas volume.

4. An energy capsule as in claim 3 wherein a metal shield is embedded in said insulating material disposed in the bottom of said metal housing and encompassing said conductor whereby external radiation is reduced and also the radiation level of said capacitor.

5. An energy capsule as in claim 4, and a voltage regulator in said capsule based vupon the Geiger effect in gas conduction.

References Cited by the Examiner UNITED STATES PATENTS 2,789,241 4/1957 Frey l 3l03 X 3,005,942 10/ 1961 Perdreaux 3l03 CHESTER L. JUSTUS, Primary Examiner.

.G. M. FISHER, Assistant Examiner. 

1. IN AN ENERGY CAPSULE, A METAL HOUSING HAVING AN OPENING IN THE TOP AND THE BOTTOM THEREOF, A FLEXIBLE DISC OF INSULATING MATERIAL HAVING A CENTRAL APERATURE COVERING THE TOP OPENING, A METAL PLATE COVERING THE OPENING IN THE BOTTOM OF SAID HOUSING, INSULATOR MATERIAL DISPOSED IN THE BOTTOM OF THE HOUSING ADJACENT SAID PLATE, A CONDUCTOR ROD HAVING A POINTED TIP AND A FLARED BOTTOM DISPOSED CENTRALLY IN SAID HOUSING, THE FLARED ROD BOTTOM BEING EMBEDDED IN SAID INSULATOR MATERIAL, A COATING OF RADIOACTIVE ELECTRON EMITTING MATERIAL ON THE FLARED ROD BOTTOM, AN INSULATOR, SAID INSULATOR POSITIONED IN SAID METAL HOUSING ADJACENT TO SAID FLEXIBLE DISC AND ENCOMPASSING A PORTION OF SAID ROD ADJACENT SAID POINTED TIP WHEREBY A TOP CHAMBER IS FORMED BETWEEN SAID FLEXIBLE DISC AND SAID INSULATOR AND A CENTRAL CHAMBER IS FORMED BETWEEN SAID INSULATOR AND SAID INSULATING MATERIAL DISPOSED IN THE BOTTOM OF SAID METAL HOUSING, A CAPACITOR, SAID CAPACITOR FIXED IN SAID CENTRAL CHAMBER AND CONNECTED BETWEEN SAID CONDUCTOR ROD AND SAID METAL HOUSING, SAID POINTED TIP OF THE CONDUCTOR ROD PROTRUDING INTO SAID TOP CHAMBER, AND A METAL BUTTON MOUNTED IN SAID FLEXIBLE DISC FOR MOVEMENT INTO CONTACT WITH SAID POINTED TIP. 